Glittering articles have been produced for many years. The articles often are used for decorative purposes. Customarily, glitter has been produced by incorporating or suspending metallic particles into a substrate. Flakes of finely divided metallic particles such as copper, silver, aluminum, or the like have been incorporated into polymeric substrates as documented by U.S. Pat. Nos. 5,470,058, 5,362,374, 5,202,180, 3,988,494, 3,987,229, and 3,010,845. Finely divided metal flakes have also been placed in a coating substrate--see U.S. Pat. Nos. 5,276,075, 3,988,494, 3,697,070, and 3,692,731. In another approach, U.K. Patent No. 1,516,686 discloses a glittering product that is produced from non-metallised and non-reflective substrate on which a metallic, reflecting film is hot pressed, simultaneously forming an impression or copy from a printing block. The copy is engraved with adjacent zones formed by networks with varying orientation and which are too fine to be seen by the naked eye, the result being the formation of glittering zones created by the valley and peaks of the networks. The glittering zones (i.e., iridescence) are produced on a non-metallised and non-reflective substrate.
Cube-corner articles have been used in the retroreflective field for many years. See, for example, U.S. Pat. Nos. 5,138,488, 4,775,219, 4,588,258, 4,066,331, 3,923,378, 3,684,348, 3,541,606, and Re 29, 396. The articles are capable of returning substantial quantities of incident light back towards the light source, and therefore have become commonly used on road signs, barricades, and safety vests.
FIGS. 1 and 2 illustrate an example of a cube-corner retroreflective sheeting, noted generally by numeral 10. The array of cube-corner elements 12 project from a first or rear side of a body portion 14 that includes a body layer 18 (also referred to in the art as an overlay) and may also include a land layer 16. Light enters the cube-corner sheeting 10 through the front surface 21; it then passes through the body portion 14 and strikes the planar faces 22 of the cube-corner elements 12 to return in the direction from which it came as shown by arrow 23.
FIG. 2 shows the back side of the cube-corner elements 12, where each cube-corner element 12 is in the shape of a trihedral prism that has three exposed planar faces 22. The cube-corner elements 12 in known arrays are typically defined by three sets of parallel v-shaped grooves 25, 26, and 27. Adjacent planar faces 22 on adjacent cube-corner elements 12 in each groove form an external dihedral angle (a dihedral angle is the angle formed by two intersecting planes). This external dihedral angle is constant along each groove in the array. This has been the case for a variety of previously produced cube-corner arrays.
Although cube-corner sheeting is known to provide very effective retroreflectivity, the sheetings that have been heretofore developed are not known for displaying a glittering appearance.